I think what they are talking about are the sliders in the intel box. Load up the island in the mission editor. In the upper right hand corner, there is a box. Click it. A popup should appear. Towards the bottom should be four sliders. You will notice on each slider there are sixteen setting lines. The first slider decides the weather, place this where you want it. The second one decides fog. Place this slider anywhere from the 12th to the 16th line to the right.. The third slider should look like the first one, and the fourth slider should look like the second one. Hit preview. As soon as the game is ready, hit escape-options-video settings. Once there, you should see a slider that says visibility. Move this all the way to the left. You should now be ready to use the island.
I hope that helps you. If my instructions are unclear, say so and I will try to clarify.
EDIT:
Beaten again, although Rujik's way requires an init file, mine doesn't.